Microsurgical procedures frequently require precision cutting and/or removing of various body tissues. For example, certain ophthalmic surgical procedures require cutting and removing portions of the vitreous humor, a transparent jelly-like material that fills the posterior segment of the eye. The vitreous humor, or vitreous, is composed of numerous microscopic fibrils that are often attached to the retina. Therefore, cutting and removing the vitreous must be done with great care to avoid traction on the retina, the separation of the retina from the choroid, a retinal tear, or, in the worst case, cutting and removal of the retina itself. In particular, delicate operations such as mobile tissue management (e.g., cutting and removal of vitreous near a detached portion of the retina or a retinal tear), vitreous base dissection, and cutting and removal of membranes are particularly difficult.
Conventional vitrectomy probes can be divided into two types: axial or “guillotine style” probes and rotational probes. An axial or guillotine style probe has an inner cutting member that reciprocates in a translational manner along its longitudinal axis. The inner cutting member is positioned within an outer cutting member that includes a port at its distal end. Vitreous humor and/or membranes are aspirated into the open port of the outer cutting member. The vitreous and/or membranes are cut as the inner cutting member reciprocates. The cut tissue is then aspirated away from the eye. The inner cutting member may reciprocate at a rate between several tens to several hundred times per second. The reciprocal movement of the inner cutting member may produce an undesirable pumping action or pulsatile flow that pushes fluid out of the port as the inner cutting member moves towards the port and draws additional fluid into the port as the inner cutting member moves away from the port.
A rotational or rotary probe has an inner cutting member that rotates at a high rate around its longitudinal axis. Continuous rotation of the inner cutting member may cause undesired winding and/or tearing (as opposed to cutting) of the vitreous collagen fibers. Some rotational probes have attempted to address this issue by replacing continuous rotation of the inner cutting member with limited rotary action drive mechanisms that limit angular rotation. Limited rotary action drive mechanisms, however, could not be implemented in small gauge vitrectomy probes because of spiral torsional failure during reciprocation of the inner cutting member.